Conventional small-sized, light-weighted power supply apparatuses for arc-utilizing apparatuses are arranged such that an AC input voltage applied thereto is converted into a DC voltage by an input rectifier. The resultant DC voltage is then converted into a high-frequency voltage by an inverter. The high-frequency voltage is then voltage-transformed to a voltage having a desired value by a high-frequency transformer. The voltage-transformed high-frequency voltage is converted back into a DC voltage by an output rectifier, which DC voltage can be applied to a load. Japanese Patent Application Publication No. HEI 05-277731 A discloses an example of a power supply apparatus for arc-utilizing apparatuses, arranged based on the above-described power supply concept, which can operate from either one of two, higher and lower AC input voltages.
The power supply apparatus disclosed in Japanese Patent Application Publication No. HEI 05-277731 A is provided with a pair of inverters. For a higher AC input voltage of, for example, 400 V, applied to the input of the power supply apparatus, the two inverters are connected in series in the output of the input rectifier. If a lower AC input voltage of, for example, 200 V, is used, the two inverters are connected in parallel with each other in the output of the input rectifier. In order to prevent input voltages as applied to the respective inverters, when connected in series, from being imbalanced, a tertiary winding is provided for a high-frequency transformer connected in the output of each inverter. In addition, a diode bridge is used to convert a high-frequency voltage induced in each tertiary winding into a DC voltage, which is fed back to the input side of the inverters. More specifically, the DC voltage resulting from the high-frequency voltage induced in the tertiary winding of a first high-frequency transformer is fed back to the input of the inverter associated with a second high-frequency transformer, and the DC voltage resulting from the high-frequency voltage induced in the tertiary winding of the second high-frequency transformer is fed back to the input of the inverter associated with the first high-frequency transformer.
The power supply apparatus disclosed in this Japanese patent application publication requires tertiary windings in the high-frequency transformers, and diode bridges in association with the respective tertiary windings, which impedes reduction of size and weight of power supply apparatuses of this type.
An object of the present invention is to provide a power supply apparatus for an arc-utilizing apparatus, which can be small in size and light in weight.